The present invention relates to a process for the production of superconducting wires formed from intermetallic compounds based on Group IIA and Group IIIA elements of the Periodic Table (CAS Version), particularly magnesium diboride (MgB2).
Superconductivity is a property of many metals, alloys and chemical compounds in which the electrical resistivity of the materials vanishes and the materials become strongly diamagnetic at temperatures near absolute zero.
In order for a material to exhibit superconducting behavior, the material must be cooled below a characteristic temperature, known as its superconducting transition or critical temperature (Tc), by approximately one-half of Tc. The Tc of superconducting materials based on intermetallic compounds is approximately 20K. These intermetallic superconductors have been typically operated in a bath of liquid helium at a temperature of about 4K. It has, however, been recently reported that an intermetallic compound, specifically magnesium diboride, can have superconducting properties at-around 40K. Thus, it would be possible to utilize magnesium diboride as a superconductor by cooling with a conventional closed-cycle refrigerator, which is capable of cooling objects to 20K with no liquid cryogens.
Wires made with superconducting materials provide significant advantages over conventional copper wires because they conduct electricity with little or no resistance and associate energy loss and can transmit much larger amounts of electricity than conventional wires of the same size.
In U.S. Pat. No. 4,980,964 there is taught a method of producing a superconducting wire. The wire is produced by filling a metal tube with a powder of ceramic superconductive material, sealing the tubes ends and drawing the filled, sealed tube through die of progressively smaller size until a predetermined wire size is achieved. The tube is then subjected to heat treatment to assure necessary crystallinity in the superconductor material.
U.S. Pat. No. 5,252,550 teaches a method of producing a superconducting composite wire in which a continuously supplied metal strip is formed into a flume shape, filled with a ceramic copper oxide superconducting powder material, rolled such that ends of the strip meet to form a tube, welded to form a seam, and sintered. The tube enveloping the sintered material is then deformed to a reduced cross section and subjected to a heat treatment. The superconducting material is a ceramic copper oxide.
In U.S. Pat. No. 6,289,576 there is taught a method for drawing elongated superconductive wires. Superconducting oxidic ceramic materials are worked to filamentary conductors by a silver tube as a sintered sleeve which is brought into contact with the ceramic material in a drawing sleeve of soft annealed steel and the resulting sleeve combination undergoes drawing stages.
There has now been found a process of continuously forming a superconducting wire containing a superconducting material of magnesium diboride powder. The process provides a long length, low cost strand of superconducting wire.